Chain saws have been available for several decades. The chains used in chain saws commonly include drive links which engage into a power sprocket, connecting links and cutter elements. Such saw chains have been primarily intended for cutting wood. It has been found, however, that chain saws can be used to cut many different substances in addition to wood. Materials which can be cut by chain saw means include pumice stone, brick, tile, asbestos cement board, stucco, pipe and frame house and roof structures, which include shingles of a variety of materials including nails, joists, hangers and gravel and stone on top of built-up roofs. Firefighters have to use chain saws for cutting house structures on an emergency basis.
An extensive amount of prior art describes various chains developed for many cutting purposes. The known prior art traces attempts to develop a cutter more resistant to blunting and shock destruction than the conventional stamped-out steel cutter commonly used by the wood industry. A number of inventions relate to the shape of the cutting element and also to the use of hard metal alloy inserts, such as carbide compositions attached to steel supports. The prior art generally shows permanent attachments, that is, connecting of a hard metal insert to a body element by braising or soldering, for example. This type of structure is shown in U.S. Pat. Nos. 3,292,675, 2,976,900, 2,862,533, 2,798,517 and 4,606,253. U.S. Pat. Nos. 2,746,494 and 2,994,350 describe hard metal cutting inserts which are removable from the cutter body. The known prior art is primarily concerned with cutters having cutting edges which are rectangular or L-shaped, and which, due to the rapid movement of the chain, act as chisels, chipping away the material.
No prior art teaches the concept of effectively protecting the entire scope of the cutting edges from the effects of sudden impacts of hard material. Only U.S. Pat. Nos. 3,292,675 and 4,606,253 acknowledge or describe an attempt to remedy the impact problem. The '253 patent concerns a chain using a carbide composition insert supported by a steel element having two parallel flanks and made from a single piece of bent steel of relatively low hardness, intended to withstand the impact shock without detaching the cutting insert. This design, however, does not protect the carbide insert from frontal impact. The softness of the steel from which the chain links are manufactured causes rapid lengthening of the chain during cutting, which in turn may cause the chain to disengage itself from the leading groove of the saw bar or the sprocket or both.
The '675 patent claims a chain adequate for cutting through the mixed materials. It concerns an L-shaped cutter element of carbide with the cutting edge only partially mating with a notch in an L-shaped body of the cutting link.